The present invention relates to oscillators and, more particularly, to high frequency dielectric resonator stabilized oscillators incorporating dielectric resonator discs, cylinders, stabs, etc. for determining the resonant frequency of the oscillator.
In the past, one method of constructing high frequency oscillators has been to utilize Gunn diodes and microwave transistors mounted in various transmission line resonators. However, such transmission line resonator oscillators have poor temperature stability because of the temperature dependence of the semiconductor devices used in the construction thereof, the poor temperature sensitivity of the transmission line mediums and the low quality (Q) factor of the transmission line resonators. Furthermore, the sensitivity of the oscillator to the difference in device semiconductor characteristics from one semiconductor device to the next and the sensitivity to the transmission line resonator dimensions has made such transmission line resonator oscillators expensive to mass produce since very close tolerances are required for the transmission line resonator parts and the semiconductor device characteristics. Because of the low Q of the transmission line resonators, the oscillator frequency stability, FM noise, pushing, pulling and other characteristics are not as good as required for many applications. Hence, a less expensive and better performing fundamental resonator oscillator is needed.
In recent years, dielectric resonators of high dielectric constant (E.sub.r =3.sub.8 is typical), low-loss and high temperature stability have been developed to allow high frequency transistors and Gunn diode transmission line oscillators to be designed with a dielectric resonator which have high frequency stability, high Q, small size and low noise performance. The small size, simple construction and moderate bias requirements of these dielectrically stabilized oscillators give them important advantages over the aforementioned transmission line resonator oscillators as well as other cavity resonators and crystal-controlled multiplier chain types of oscillators.
Typically, commercially available dielectric resonator stabilized oscillators consist of a transistor, Gunn or Impatt diode oscillator locked to some resonant frequency by a resonant disc of dielectric material. The disc is coupled to a microstrip line or lines to provide the necessary positive feedback for oscillation. One type of such disc commercially available is made of Barium Tetratitanate material.
Contemporary dielectric resonator stabilized oscillators (DRSOs) which have been sold for about the last five years are constructed by mounting the usually cylindrical shaped disc resonator on a microstrip substrate comprising the microstrip circuitry (microstrip being one type of transmission line) to which the disc resonator is electro-magnetically coupled. For optimum oscillator characteristics the disk resonator must be located adjacent the transmission line or microstrip line to provide the proper positive feedback and impedance match to the circuitry and semiconductor device. Thus, present day methods of mounting the disc resonator to the microstrip substrate is undesirable for commercial production as it requires extremely precise circuit and semiconductor device tolerances to achieve optimum performance or expensive tuning means such as adjustments in the microstrip circuitry to correct for misplacement of the disc resonator. The disc can be easily misaligned as it must typically be within 0.001 inches in both the x and y dimensions of the microstrip line to provide optimum results in most microwave circuits. This increases the production costs which is undesirable and does not allow easy adjustable tuning from oscillator to oscillator to compensate for device and production tolerance differences.
Thus, a need exists for permitting optimization of the operating characteristics of DRSOs in production assembly while minimizing operator time for optimizing these characteristics.